The present invention relates generally to methods for forming ceramified filaments from a resin and more particularly to methods for continuously processing a resinous organosilicon polymer by melt spinning into a filament followed by crosslinking and pyrolysis into a ceramic fiber in a one-step process.
Certain resinous organosilicon polymers are useful as precursors for forming ceramic fibers having a composition consisting essentially of silicon and at least one of nitrogen and carbon. These ceramic fibers are useful., for example, in composite, high temperature-resistant materials, e.g., materials made into jet engine parts.
The resinous organosilicon polymer typically contains silicon, hydrogen, nitrogen and carbon, with oxygen present as an impurity. It may also contain certain additives, such as chlorine, boron, titanium or aluminum. This resin is typically processed into a fiber by melting solid resin and then melt spinning the molten resin through a conventional spinning device called a spinnerette, to form one or more filaments which are gathered into a fiber tow. Typically this tow is taken up on a spool or reel or gathered into a loose pile. The fiber is then subjected to a cure process following which the cured fiber is subjected to a pyrolyzing operation which typically drives off the hydrogen and some of the nitrogen, silicon, carbon and oxygen as gas or vapor, to produce the ceramic fiber. Due to the marked differences in the processing speeds at which pyrolysis could heretofore be carried out in contrast with the high process speed heretofore required for successful fiber spinning, the fibers had to be wound onto a spool or otherwise gathered and later pyrolyzed in accordance with a discontinuous process which necessarily lacked efficiency.
A more detailed description of a prior art process for forming a ceramic fiber from a resinous organosilicon polymer is contained in an article by LeGrow et al, "Ceramics From Hydridopolysilazane", Am. Ceram. Soc. Bull., 66[2]: 363-67 (1987), and the disclosure thereof .is incorporated herein by reference. The use of preceramic polymers is also described in my U.S. Pat. No. 4,810,443 issued Mar. 7, 1989, which disclosure is also incorporated by reference.
Various curing procedures and curing agents of the prior art are described in U.S. Pat. Nos. 3,853,567, 4,535,007, 4,399,232, 4,310,651, 4,312,970, 4,342,712, 4,482,689, 4,340,619, and 4,693,914.
In the prior art, the preparation of ceramic fibers from preceramic polymer resins involved several separate, discontinuous steps. These included fiber spinning, fiber cure, winding of the fiber on a bobbin, transfer of fiber to a pyrolysis operation, and rewinding of the resultant ceramic fiber for further processing. These separate steps represent excessive handling which is costly and can also induce damage to the fibers at the various process steps.